Method of uniting nickel chrome steel turbine blades



May 7, 1955- P. c, DIMBERG 2,000,692

METHOD OF UNITING' NICKEL CHROME STEEL TURBINE BLADES Filed May 9, 1950 compositionv or of similar material have been Patented May 7, 1935 METHOD OF UNITING NICKEL CHROME STEEL TURBINE BLADES Paul C. Dimberg, Wauwatosa, Wis., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application May 9, 1930, Serial No. 450,974

operating shroud, lacing wire and foundation segments than has heretofore been possible, this invention contemplates plating of -the nickel chrome blades with a suitable metal. Silver has been found to be a suitable plating metal for this purpose. Since the art of electroplating is well developed no further disclosure of this feature of the invention, is necessary, as any of the well known electroplating methods may be used in carrying out this step of this invention.

According to this invention after the blades have been electroplated with silver, they are arranged and held in segmental formation in a blade spacing and angling jig which will later be described. A shroud segment I6 is then attached to corresponding ends of the blades by fusion of metal, as for instance by brazing. The brazing material may be silver solder which fuses at a temperature considerably below 1760 Fahrenheit, the melting point of silver. It has been observed that when the nickel chrome steel of which the blades are made is heated above 1700 F., grain growth may occur therein. This change of structure of the blade material greatly aiects the strength of the blades, making the same much weaker than before the heat treatment. To avoid this condition, the operator doing the brazing observes the action of the flame used in brazing the silver solder against the blades 4 Claims.

This invention relates generally to the artofv manufacturing steam turbine blade segments or the like and more particularly to a method of uniting nickel chrome steel turbine blades to form a blade segment.

Processes heretofore successfully practiced in uniting steam turbine blades of `copper nickel foundvto be quite inadequate when followed in attempting to unite blades of stainless nickel chrome steel. Such alloys as silver solder which are ordinarily utilized for the purpose of uniting blades do not adhere readily to nickel chrome steel. Further, it has been found that the strength of nickel chrome steel may be seriously impaired by reason of grain growth in the steel if it is heated, during the uniting process, materially above the minimum temperature at whichYV union with the alloy may be eiected. v

It is an object of the present invention to provide a method of uniting an alloy to a nickel chrome steel turbine' blade securely and without detrimentally affecting the internal structure of the nickel chrome steel.

According to the present invention, a nickel chrome steel turbine blade element is united to an alloy element, as, for example, silver solder, by first electroplating the nickel chrome steel blade with silver, then heating one of the elements to a temperature which is not materially and when the silver plating begins to vanish by higher than that which will cause the silver platfusion he is aware that the flame isv of such a ing to fuse and not so high as that which might', high temperature that the further use of the cause grain growth in the steel, and then bringing :flame will result in. great injury to the blades, the elements together to join them. and that he should therefore adjust the name Referring to the drawing: to a safe working temperature. This is one of Fig. 1 is a plan view of a blade spacing and the advantages of the step of silver plating the angling jig utilized in manufacturing turbine nickel chrome steel blades. blade segments. If relatively long `blades are being formed into Fig. 2 is a central vertical sectional view of blade segments, the step of providing lacing wire the showing in Fig. l, taken on line II-II thereof. tothe blades to Join them intermediate their Fig. 3 is a view showing in elevation a comlengths by fusion. of metals such as the silver pleted blade segment. y soldering described above, may also be resorted Fig. 4 is a longitudinal section of a'bla'de segto. a ment together with a portion of a blade segmentf- If the nickel chrome blades are not coated with supporting element. a metal, soldering of the shroud or lacing wire Fig. 5 is an elevation of one of the blade spacthereto effects an insecure union not having the ing and angling strips with a blade positioned in firmness of the unions contemplated for the blade one of the notc'hes provided therein. segments of this invention. In order to provide This invention contemplates the use of nickel nickel chrome blades with a metal coating, apchrome steel, stainless steel, asl a material from which the blades may be made. This steel is very tough and is especially suitable for turbine blade construction. In order, however, to proan oxide was found to have formed on the nickel duce a more effective and firmer union between chrome blades, has the other disadvantage, namethe blades and the adjacent portions of the coly,wthat many blades become cracked because of silver solder, a step referred to later in this specification. This dipping, aside from the fact that plicant has dipped them in a hot bath of molten blades were dipped for coating purposes, and thus had their strength impaired, an impairment of the strength of the nickel chrome blades just as undesirable as that due to grain growth therein.

The blades now firmly connected and assembled by the end shroud and the intermediate lacing wires, are next subjected to the step of casting on a foundation segment. This step may be carried out by an apparatus such as disclosed in Patent No. 1,620,974 to Klenk, dated March 15, 1927. Although the specific apparatus for carrying out this step is not material as far as the. present invention is concerned, the specific character of the metal of which the foundation segment is made is important. When using steel for casting in nickel chrome steel blades it was found to be difficult to'machine the steel foundation because a very tough and hard crust appears to form thereon. A composition of metal'consisting of nickel and copper has been found to be very satisfactory as a foundation segment and it has practically the same co-eilicient of expansion as steel. While the nickel copper foundation was foundto be more suitable than a foundation of steel as far as machiningproperties were concerned, it had the objectionable characteristic of having blow holes formed therein. When the nickel chrome blades are, however, electroplated as stated above with silver and thus have a silver coating on the root portion of each blade, the formation of blow holes in the foundation segment is practically eliminated. In dipping as suggested in applicants prior Patent No. 1,641,745, l

member- II suiciently withdrawn to enable the nickel chrome blades, preliminarily heated to a temperature of approximately 1200 F., in a hot bath of molten silver solder at the required temperature of approximately 1500 F., the surfaces of the blades so treated were found to become coated with an oxide. Since the temperature of the molten nickel copper alloy which forms on cooling the preferred foundation segment of this inventiomis as high as the above described dipping temperature, it may be that an oxide similarly tends to form on the root portion of the ture and the mold must be dry and free frommoisture. This is another advantage of silver plating the nickel chrome steel blades.

The improved blade spacing a'nd angling jig, already referred to, will now be described in detail. Referring to Figs. 1 and 2 it will be seen that the jig consists of two frame portions, I and II cast of a suitable metal. The cooperating jig frame II is slidingly associated with v`the main the high temperature of the bath in which thel shaped stop portions 2 and I2 of the frames I and II respectively. The arcs of these stop portions are concentric with the recesses in which strips 3 and 4 are received. The arc shaped ste; portion 2 of the main jig frame is provided with a plurality of threaded bores for receiving studs 22 on which a clamping plate 2| is slipped for the purpose of adjustably pressing the root ends of the blades when positioned in the jig against the strip 3, by turning the wing nuts 23 on the studs 22. In order to avoid damaging the blades it is well to place a strip of asbestos 20 between the clamping plate 2| and the adjacent edges of the blades.

The cooperating jig frame I I is slidably removable from the main frame I by reason of the bar 5 already described. In order to hold the frame I I in a desired position with respect to the frame' I or on the bar 5, the frame I is provided with transversely directed pins 'I which form the axes of links 8 having at their other ends threaded tenons which receive wing nuts I0.' These nuts engage the outer or straight portion of the frame II. 'I'he inner edge of frame IIy is arc shaped and a plurality of holes I3 are provided to decrease the arc surface of this edge for purposes 'of heat dissipation, during the brazing operation. A metal strip I4 is secured against this edge of the frame II by means of screws I5. The frame- II has an inner outline as shown by the dotted lines in Fig. 1 for the purpose of reduced cost and weight of the jig.

Ihe operation of the device is as follows: The clamping plate 2| is rst removed and the frame positioning of the previously silver plated blades I1 in the notches 21 in the strips 3 and l. The

.clamping plate 2| is then applied to the frame I so as to press slightly against the blades. The frame I I carrying a shroud ring segment I8 is then slid closer to frame I by operating wing nuts I0 until the root ends of the blades uniformly bear against the stop portion 2 and the other end of the blades uniformly bear against the proper portions of the shroud I6 as correctly determined by the notched strip 4. v'Ihe notched strip 4 used for spacing and angling the blades at the shroud end thereof is similar to the strip 3 at the root end of the blades. The advantage in using the strip l resides in the fact that a plain shroud may be used instead of one that has been provided with pressed out portions that conform to the shape and desired angling and spacing of the blades in which the shroud end of the blades were formerly held. For the shroud when provided with thenecessary depressed portions is strained and the presence of the strain is later found to be detrimental and injurious to the shroud when heat is supplied thereto to unite the vblades and shroud by fusion of metals as for instance by silver soldering. s

Lacing wires are then laid in notches in the edges'of .the blades or pushed through openings in the blades as shown. The blades are then jig frame I by being provided with a rectangular/ .gbl-Zed jor soldered as by vsilver soldering to the of the blades are positioned in the notches in thel strips,` the opposite edges of the blades'v will "be `parallel to the base of the frame I and will be disposed about as high as the top sof the aro,

shroud and lacing wire. 'I'he uniform llets now obtained in brazing or soldering the'lacing wire to nickel chrome steel `blades after they have been silver plated according to this invention are illustrated by the stippled areas surrounding the lacing wire in Figs, 2, 3 and 4. After the shroud has been soldered to the blades the blade segment is removed from thejig by first removing the clamp- Y Y ingV plate 2| and then withdrawing frame II from 5 its Aengagement with the shroud I0.

A foundation segment is then cast on the root end of the blades by using any suitable apparatus as for instance that disclosed in the patent to Klenk No. 1,620,974 already referred to. A composition metal consisting of nickel and copper is preferable to steel as the foundation metal, because it is more easily machined. The specic machining of the foundation may take the form shown by in Fig.' e to cooperate with similar machining in the final supporting element 26. After these machined portions of the foundation segment and supporting element have been brought into engagement, calking strips 24 may be used to hold the assembled blade segments in proper position.

It should be understood that itis not desired to limit the invention to the exact steps of the process and to the exact details of construction and operation of the apparatus herein shown and described, for various modifications within the scope of the claims may occur to persons skilled in the art.

It is claimed and desired to secure by Letters Patent:

l. The method of making a steam turbine blade segment, comprising shaping'a plurality of turbine blades from nickel chrome steel, electroplating said blades with silver, arranging said plated blades in position to constitute a segment oi turbine blading, disposing a shroud ring segment in contact with the ends of said blades, heating the contacting end oi each blade and the adjoining shroud ring' portion to a temperature not materially greater than that at which the silver plating on the blade end fuses, and applying silver solder to said heated blade end and said shroud ring portion to join them.

2. The method of uniting a nickel chrome steel turbine blade element to an alloy element, comprising electroplating said blade with silver, heating one of said elements to a temperature above the melting point of the silver plating but below that which might cause grain growth in -said nickel chrome steel blade, and then bringing said blade and said alloy element into close contact to Join them.

3. The method of uniting a nickel chrome steel turbine blade to an alloy, comprising electroplating said blade with silver, fusing said alloy, and casting said fused alloy on to said plated blade at a temperature above the melting point of the silver plating but below that at which grain growth might occur in the nickel chrome steel blade.

4. The method of joining a cooperating element to a nickel chrome steel turbine blade, compris.- ing electroplating said blade with silver, applying said cooperating element to said blade, heating said blade at the point of juncture with said cooperating element to a temperature not materially greater than that at which said silver plating begins to fuse, and then applying silver solder to said heated point of juncture to unite said cooperating element to said nickel chrome steel blade.

. PAUL C. DIMBERG. 

